The present disclosure relates generally to systems and methods for performing magnetic resonance (MR) studies. More particularly, the disclosure relates to systems and methods for performing magnetic resonance fingerprinting (MRF) at high field strengths, such as 4.7 Tesla (T) and above.
MR studies use the nuclear magnetic resonance (NMR) phenomenon to produce images. When a substance such as human tissue is subjected to a uniform magnetic field, such as the so-called main magnetic field, B0, of an MRI system, the individual magnetic moments of the nuclei in the tissue attempt to align with this B0 field, but precess about it in random order at their characteristic Larmor frequency, ω. If the substance, or tissue, is subjected to a so-called excitation electromagnetic field, B1, that is in the plane transverse to the B0 field and that has a frequency near the Larmor frequency, the net aligned magnetic moment, referred to as longitudinal magnetization, may be rotated, or “tipped,” into the transverse plane to produce a net transverse magnetic moment, referred to as transverse magnetization. A signal is emitted by the excited nuclei or “spins” after the excitation field, B1, is terminated, and this signal may be received and processed to form an image.
Though the most-common clinical MR systems utilize a static magnetic field strength of 1.5 Tesla (T) or 3.0 Tesla (T), high field, preclinical (≥4.7 T) MRI scanners are also available. In contrast to clinical MRI scanning, high-field preclinical MRI studies are often quantitative by nature and may require assessment of multiple imaging parameters during a single scanning session. These quantitative preclinical MRI studies provide the opportunity to assess pathophysiologic changes associated with disease progression and therapeutic efficacy. In addition, rigorous validation of these MRI assessments has the potential to inform future clinical imaging studies. Therefore, a significant effort is ongoing to develop robust and effective acquisition and reconstruction techniques that can be used routinely in clinical practice preclinical MRI acquisition and reconstruction techniques.
Conventional MRI quantification methods are typically based on linear or nonlinear curve fitting to various MRI models. The implementation of these established model-based methods, such as T1 and T2 relaxation time estimation, are straightforward. However, these conventional quantification methods are susceptible to multiple sources of errors including cardiac and respiratory motion artifacts, as well as, inhomogeneity in the main magnetic field (B0). Importantly, the potential for these errors are significantly increased on high field preclinical MRI scanners, where B0 inhomogeneities are increased, and other confounding factors can also be present. In addition, temporal errors can be observed in high-field studies that require multiple imaging parameter estimates (ex. diffusion and perfusion) and extended or sequential scans. Therefore, new MRI acquisition and reconstruction methods for preclinical imaging applications are needed that are not as susceptible to these error sources and can readily obtain estimates of multiple imaging parameters simultaneously.